In a wideband wireless communication system, the channel signatures in different frequency bands may be mutually uncorrelated. That is, the behavior of the wireless channel between two devices in one frequency band is different than that in another frequency band. Consequently, it is difficult to apply beamforming techniques in such a system due to the lack of accurate channel information in some frequency bands. Estimating the channel information in other frequency bands using, for example, feedback techniques, is one solution but it involves adding overhead to the communication link in one direction.
In time division duplex (TDD) systems, the uplink channel coefficients describing the channel in the uplink direction (e.g., from a wireless client device to a base station) are strongly correlated with the downlink channel coefficients describing the channel in the downlink direction (from the base station to the wireless client device). There are ways to exploit this property in order to estimate the channel information in any frequency band for purposes of computing beamforming weights used for beamforming transmissions from one device to another device.